cryptodev: Handle unexpected request to avoid crash

Generally guest side should discover which services the device is
able to offer, then do requests on device.

However it's also possible to break this rule in a guest. Handle
unexpected request here to avoid NULL pointer dereference.

Fixes: e7a775f ('cryptodev: Account statistics')
Cc: Gonglei <arei.gonglei@huawei.com>
Cc: Mauro Matteo Cascella <mcascell@redhat.com>
Cc: Xiao Lei <nop.leixiao@gmail.com>
Cc: Yongkang Jia <kangel@zju.edu.cn>
Reported-by: Yiming Tao <taoym@zju.edu.cn>
Signed-off-by: zhenwei pi <pizhenwei@bytedance.com>
Message-Id: <20230803024314.29962-3-pizhenwei@bytedance.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

backends/cryptodev.c

@@ -191,6 +191,11 @@ static int cryptodev_backend_account(CryptoDevBackend *backend,
     if (algtype == QCRYPTODEV_BACKEND_ALG_ASYM) {
         CryptoDevBackendAsymOpInfo *asym_op_info = op_info->u.asym_op_info;
         len = asym_op_info->src_len;
+
+        if (unlikely(!backend->asym_stat)) {
+            error_report("cryptodev: Unexpected asym operation");
+            return -VIRTIO_CRYPTO_NOTSUPP;
+        }
         switch (op_info->op_code) {
         case VIRTIO_CRYPTO_AKCIPHER_ENCRYPT:
             CryptodevAsymStatIncEncrypt(backend, len);
@@ -210,6 +215,11 @@ static int cryptodev_backend_account(CryptoDevBackend *backend,
     } else if (algtype == QCRYPTODEV_BACKEND_ALG_SYM) {
         CryptoDevBackendSymOpInfo *sym_op_info = op_info->u.sym_op_info;
         len = sym_op_info->src_len;
+
+        if (unlikely(!backend->sym_stat)) {
+            error_report("cryptodev: Unexpected sym operation");
+            return -VIRTIO_CRYPTO_NOTSUPP;
+        }
         switch (op_info->op_code) {
         case VIRTIO_CRYPTO_CIPHER_ENCRYPT:
             CryptodevSymStatIncEncrypt(backend, len);